My SMG gearbox light comes on occasionally, INPA reporting that the pump has been on too long. I've replaced the salmon pink relay but that's had no effect.

After one such incident, with INPA hooked up to the car I reset the errors and then repeatedly changed from 1st to 2nd and back again, watching the hydraulic pressure drop from ~75bar to ~50bar over the course of about 6 gear changes, and then saw it rise again taking about six seconds, hearing the pump run at the same time. Having done this several times the pressure failed to rise, the pressure instead staying at ~50bar. The pressure didn't so much as twitch, and I didn't hear the motor running. After a little while (~15 seconds, but I wasn't timing it) the gearbox warning light came on again reporting the normal fault. A few seconds later the pressure then rose, taking the normal six seconds to reach ~75bar.

The conclusion here is that the motor driving the pump wasn't working properly.

I've obtained a failed SMG pump unit from my local BMW specialist, and I've been stripping it down to refurb it as a replacement for my failing unit.

I didn't take photos of the motor removal (I'll take some when I replace it), but see below for the state of the motor commutator.

That is now being rewound, with the commutator, brushes and bearings being replaced for <£150 (I'll post the precise price when I get it back). In the meantime, I thought I should check that the pump itself is OK.

The cover (which serves as a sump for the hydraulic fluid) needs to be removed.

Unscrew the pressure accumulator first, then remove the six torx bolts holding the cover on. The cover has a rubber 'o' ring style seal which should come away without any issue and can be reused.

This will reveal the pump with it's inlet filter in place.

This simply pulls off. Note that in the photo below I'd already removed the two torx bolts holding the pump in place.

Removing the two hex bolts to reveal the innards reveals the pump to be a roots style pump.

This was in perfect condition, so I've replaced it, and cleaned up the pump assembly, and I'm awaiting the return of the motor, very optimistic that it is the cause of the SMG unit failure.

I'll get my local BMW specialist to actually swap out my SMG unit with this one, which I suspect will be suffering from exactly the same fault.

I've wondered about this for some time, nice job! I never pulled the motor apart, have pulled the pump apart, tested all solenoids, etc.
I will say if you go to pull the gear pump apart, witness mark everything, and be careful the gears don't just fall out. they appear symmetrical, but these things wear into each other, the steel gear to the brass bushing/bearing it rides in, so if you put it in upside down, it will look fine, but will create extra bearing wear that won't help longevity of the pump. Also be careful of the uniquely shaped rubber seals you see around the gears. They can tend to stick to one/both sides: if you rip one, I doubt you'd ever find a replacement, and at 1200 psi, hoping a torn one will seal ok is folly.
The pump I dis-assembled looked even better than this one, less discoloration of the gears/oil. It was fine, as the owner replaced it with a new one and that didn't solve the problem.
Honestly I think the whole unit runs way to hot: a bad symbiotic relationship between a motor that runs hot and a gear pump that eventually runs hot.

Actually, a properly designed hydraulic system should go millions of cycles of uninterrupted use. I think the temps are a factor, especially for the electric motor, so excited about how this goes.
If this works, also probably we could investigate and spec a replacement 12v motor and have very little downtime, although I like the value and ability to have a local shop repair the motor where possible.

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Quote:

Originally Posted by Simann

Thinking about how many thousands upon thousands of shifts per year the SMG system has to deal with, I would say this is purely wear and tear. Of course the easy and most costly way of repairing is always replacing with new...but if you can fix the unit for $300 USD and be out of a car for 2 weeks at most....that's a deal!

Curious, did your motor shop tell you the rewind was necessary from an armature test? Brushes and commutator cleanup would be relatively quick and inexpensive, but if the armatures are burning up, that will be more costly. And it probably says a lot about the severity of use/temp or call into question the duty cycle sizing.

For the cost involved, once I saw the state of the commutator I just asked them to replace everything; windings, commutator, brushes, bearings, seals. Unfortunately they lost the end seal! It's only a dust seal, so a bead of silicone sealant will be OK, but rather annoying. I hope to receive the motor back on Monday.

Including VAT and shipping this has cost £183, so I hope it proves worthwhile. I've also got a replacement temperature sensor (p/n 13-62-1-709-966) from BMW for £26.

It would be nice if we could find a suitable brushless motor replacement.

I fly radio controlled helicopters for a hobby where brushless motors are the norm, so this thought did cross my mind. Considering that the SMG pump pulls ~20A at 12V, ie 240W, you get easily get a motor of double the power that's tiny. Below is an Align 450MX rated at 500W continuous, 750W peak.

Unfortunately at 12V, this motors runs at 41000RPM, so a gearbox would be required. An awkward complication, and itself then prone to failure!

Sorry for the quickfire posting, but I just found THIS reporting that BMW have issued a recall on M5/M6 models due to SMG motor failure. For the M5 you can buy the motor for the SMG pump for $330; see HERE. That's less than this rewind has cost me!

Sorry for the quickfire posting, but I just found THIS reporting that BMW have issued a recall on M5/M6 models due to SMG motor failure. For the M5 you can buy the motor for the SMG pump for $330; see HERE. That's less than this rewind has cost me!

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